1. Field of the Invention
The present invention relates to a method of producing boron alloy with a boron content between about 0.001% and 15% by weight and a product produced by the method. Although not so limited, the method of this invention has particular utility in the production of both crystalline and amorphous boron alloys by in situ reduction of a boron compound in a metallic melt.
2. Description of the Prior Art
Boron is a metalloid and exhibits properties of both metals and non-metals. Consequently, when boron is employed in an alloy composition, the alloy can be further treated to have properties of metals and/or non-metals.
A ferro-boron alloy melt maintains the crystalline structure of iron upon solidification. Boron employed in the alloy will increase strength, hardenability, toughness, drawability, thermal stability and enamelability. Crystalline boron alloys are employed to make, for example, wire or tools.
A ferro-boron alloy melt containing greater than 1.4% by weight boron can be further treated to form a solid amorphous structure. These amorphous alloys are being investigated for use in electrical applications because it has been found that amorphous ferro-boron alloys have lower core loss than conventional silicon steel employed for the same purpose. For example, an amorphous ferro-boron alloy containing iron, silicon, boron and carbon may have potential application for making transformers or high frequency switching cores.
Because some non-ferrous alloys can be further treated to yield an amorphous material irrespective of the amount of boron, no significant comparison can be made between the ferro-boron alloys and the non-ferrous boron alloys.
A crystalline non-ferrous boron alloy, for example, an alloy containing primarily boron, manganese, chromium, nickel, and cobalt can be used for die-casting a case or strap for a watch.
On the other hand, a non-ferrous boron alloy containing, for example, a nickel base aluminum alloy can be further treated to form an amorphous material which can be used to make razor blades or metallic belts for automobile tires.
Boron occurs in many forms such as, for example, boron oxide, boric acid, sodium tetraborate (borax), calcium metaborate, colemanite, rasorite, ulexite, probertite, inderite, kernite, kurnakovite and sassolite. These impure compounds are processed to nearly pure boron by mineral processing companies. The boron oxide is converted to an iron-boron alloy containing typically 18% boron by special reduction processes. The processed iron-boron alloy is sold to foundries and steel plants, as an additive for a ferrous melt as is disclosed in the following patents:
U.S. Pat. No. 1,562,042 teaches the conventional ferro-boron additive which is later added to the melt steel. The additive contains approximately 18% boron with the remainder being predominantly iron and a small amount of aluminum. The additive is made by mixing boron oxide, aluminum, and ferric oxide into a briquette and igniting the briquette such that an alumino-thermic reaction occurs, forming the ferro-boron additive. The additive is shipped to various steel mills or foundries to supplement the melt steel in amounts such that approximately up to 3/4 of a percent by weight of boron is alloyed with the final steel.
U.S. Pat. No. 2,616,797 also employs a thermite reaction for producing a ferro-boron alloy additive containing 1.5 to 2.8% boron by weight which is later added to molten steel to increase strength and hardenability. The alloy additive, when mixed with the steel, contains approximately 0.01 to 0.03% boron by weight.
These last two noted patents teach an additive that is employed to make a crystalline ferro-boron alloy. Nevertheless, the additive of U.S. Pat. No. 1,562,042 can be employed to make an amorphous ferro-boron alloy because the additive in briquette form contains 16% boron by weight.
The following U.S. patents teach a process for converting a ferro-boron alloy containing greater than 1.48 boron by weight into an amorphous alloy and are hereby incorporated by reference:
U.S. Pat. Nos. 4,133,679 and 4,255,189 teach a typical amorphous boron alloy composition containing 6-15 atom percent boron and including either molybdenum or tungsten with the remainder being at least one of iron, nickel, cobalt or manganese. These elements are melted together and spun as a molten jet by applying argon gas at a pressure of 5 psi. The molten jet impinges on a rotating surface forming a ribbon which is extracted and further treated.
Other patents disclose the use of boron in ferrous melts for a wide variety of purposes as noted by the following patents:
British Pat. No. 1,450,385 and U.S. Pat. No. 3,809,547 disclose the employment of boron compounds which are introduced into a ferrous melt as a fluxing agent for the slag. Neither of these patents discloses recovering boron from the boron compounds for the purpose of alloying the boron with the iron.
U.S. Pat. Nos. 1,027,620 and 1,537,997 disclose the addition of a boron compound to molten iron for the purpose of removing phosphorus, sulfur and nitrogen by chemically reacting boron with these elements found in the iron melt and forming a slag which is removed before pouring. Neither of these references teach recovering the boron from the boron compound such that the boron is capable of alloying with the iron. To the contrary, these references teach chemically reacting the boron to form a slag which is separated from the molten iron. Additionally, '997 teaches reducing the nitrogen content in the melt to less than 0.0015%.
East German Pat. No. 148,963 discloses the addition of boron oxide to molten steel in a furnace or ladle to obtain a total boron content of 30 to 160 parts per million. The boron addition acts as a chip breaker and increases machinability of the steel. It is apparent that very little boron is recovered from the boron compound because only a small amount of boron is present in the steel.
None of the above mentioned references teach reducing a boron compound with a reductant in a melt to form a boron alloy.
Although boron oxide is not employed to make stainless steel, the Argon-Oxygen Reactor (AOR) or the Argon-Oxygen Decarburization (AOD) process to make stainless steel does employ a reductant to reduce chromium, iron or manganese oxides back into the steel melt. This improves the recovery of chromium, iron or manganese over the conventional electric furnace process of making stainless steel. The following reference describes the conventional AOR:
"Making Stainless Steel in the Argon-Oxygen Reactor at Joslyn" by J. M. Saccomano et al, published in Journal of Metals, Feb. 1969, pages 59-64 disclose a process for refining a ferrous melt containing chromium by introducing an argon-oxygen gas into the melt to decarburize the melt.
In the AOR process for stainless steel, usually about 1-2% by weight of the melt is lost to the slag as oxides during the decarburization step and recovery of elements (chromium, iron, and manganese) from these oxides is very efficient using lime, silicon and sometimes aluminum. Scrap and ferro-alloys containing the metallic elements to make stainles steel are a more cost effective source for these elements than using oxide and reductant additions. However, in the case of ferro-boron, the reduction of the boron compound in a AOR type vessel using a strong reductant is economically favorable. Theoretically, reduction of one pound of boron from boron oxide requires 1.95 lbs of silicon or 2.50 lbs of aluminum. The reduction of boron oxide using silicon as a reductant in a mixing vessel is not immediately obvious because it is a very stable oxide (more stable than chromium oxide and about the same stability as silicon oxide). Also refractory erosion was believed to be a problem when boron oxide would be added to slags at conventional steel making temperatures. Therefore, it has always been the practice of the industry to purchase and employ ferro-boron as an additive to the melt.
Accordingly, the need exists for a process of reducing inexpensive boron compounds to recover boron which can be alloyed with other metals.